The charge unit type MT 9002 SN manufactured by Robert Bosch GmbH has a charge circuit for radio telephone equipment of this type. This known charging circuit utilizes an upwards d.c. voltage converter and correctly charges a storage battery in spite of input d.c. voltage that may fluctuate from, for example, 8 to 15 volts. This known charging circuit, however, cannot regulate out the effect of voltage fluctuations over a substantially greater range.